Selective solvent extraction



2 Sheets-Sheet 1 3m mm J. Q. COPE ETAL SELECTIVE SOLVENT EXTRACTION OF PETROLEUM EkzEuEm Jan. 12, 1954 Original Filed Aug. 1'

HOJQVELLXE] Inventors JOHN Q. COPE WILL/AM H CLAUSSEN Jan. 12, 1954 J. Q. coPE ET AL SELECTIVE SOLVENT EXTRACTION OF PETROLEUM 2 Sheets-Sheet Original Filed Aug. 1'7, 193'! N WE F Ta 1 BEN 3! m P 3 Em- 8? M" 00 sg m no 111T #9 J5 Q 2.. S -m\ 5 EZEE 1 U 1 2 8K NT QT x 62" a In ven Iors JOHN G. COPE W/L IAM H. CLAUSSEN Reissued Jan. 12, 1954 UNITED STATES PATENT OFFICE sensor-IVE SOLVENT Ex'rasc'non F PETROLEUM Original No. 2,215,915, dated September 24, 1940,

Serial No. 159,522, August 17, 1937. Application forreissue April 9, 1953, Serial No. 347,860

8 Claims.

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter-printed in italics indicates the additions made by reissue.

This invention relates to a process of refining petroleum with a selective solvent. More particularly, it involves a process of treating normally liquid petroleum hydrocarbons in vapor phase 'with a liquid phase selective solvent to effect a more eflicient separation of the hydrocarbon components into fractions of different chemical As'is wellknown, normally liquid petroleum contains a complex mixture of hydrocarbons of diflerent types. For example, certain natural petroleums are known to contain a minor percentage of aromatic hydrocarbons and a major proportion of paraflins and/or-naphthenes having five, six and seven carbon atoms in'the naphthene ring. Because of close similarity in properties it has been very difllcult to separate these hydrocarbons according to their chemical types. Liquid phase extraction oi petroleum oils with selective solvents at temperatures substantially below the point at which the solvent is completely miscible with the oils, constitutes one known method of refining petroleum and separating aro-- matic and/or naphthenic hydrocarbons from the remaining oil. Although such a process produces an extract containing relatively more aromatic and/or naphthenic hydrocarbons and a rafiinate relatively more paraflinic in nature, the separation is only qualitative and yields fractions containing substantial quantities of hydrocarbons which it was desired to eliminate.

It is a well accepted general rule in the art of selective solvent refining that an increase in the temperature of extraction, although it increases the'yield of extract obtained, decreases the selectivity of a given solvent and yields an extract in Y which the separation betwen aromatics and/or naphthenes on the one hand and parafiins on the other hand is less sharp than obtained at lower temperatures. That is, as temperature of extraction is increased, the yield of railinate is lowered and the extract contains more and more of the hydrocarbons which it is desired to keep in the raffinate. When the temperature of extraction is lowered, the yield of rafllnate increases but it contains an'increased amount of the type or hydrocarbons (e. g., aromatic and/or naphthenic) which it is desired to retain in the extract. Accordingly, it has heretofore been regarded as necessary to adopt a temperature intermediate the above mentioned high and low extremes such that a given solvent will yield a satisfactory quantity of raflinate and yet also give a reasonably efllcient separation or refinement of the petroleum oils.

We have discovered that by increasing the temperature of extraction to the boiling point of the hydrocarbons being extracted, a remarkable and lectivity of the solvent extraction process is produced. Y

Accordingly, an object of the present invention is to provide a simple, eifective and improved process of refining petroleum with a selective solvent.

Another object 'is to provide a process of refining petroleum with a selective solvent by counter currently contacting a normally liquid petroleum fraction with a liquid phase selective solvent having a'preferential solvent action for one class of. carbon compounds such as aromatics, at a temperature no lower than the initial boiling point of said petroleum fraction under the conditions of extraction and preferably no lower than the dew point of the petroleum fraction.

A further object is to provide a single multistage extraction process forcontinuously separating petroleum into a plurality oi separate portions comprising a fraction highly aromatic in ly liquid fraction of natural petroleum containing parafiinic compounds having boiling points as much as 20 to F. higher than the lowest boiling aromatic compound present. 1

An additional object of the invention is to provide a process capable of effecting quantitative separation of aromatics from a fraction of natural petroleum containing a minor proportion of hydrocarbons of the aromatic type. A further object of the invention is to provide 1mproved selective solvents for extraction of petroleum.

In the drawings,

Fig. 1 is a diagrammatic flow sheet illustrating a multi-stage vapor phase selective solvent extraction process embodying the principles of this invention.

Fig. 2 is a diagrammatic illustration of a process utilizing a single stage vapor phase contacting tower for carrying out the selective solvent extraction process of this invention.

Briefly, the process of this invention involves counter currently contacting normally liquid petroleum hydrocarbons with a higher boiling selective solvent maintained in liquid phase and at a temperature above the boiling point of the hydrocarbons being treated. By this process aromatic Hydrocarbons, or when desired naphthenic hydrocarbons, or both, are selectively extracted from the mixed vapor phase petroleum means may be adopted. A tower filled with suitable packing of refractory earthenware, glass, etc., comprises one effective form of apparatus for this purpose. A tower constructed in the same manner as an ordinary fractionating column oi. a bubble cap type is also an efficient means of insuring effective contact between the vapor phase petroleum and the liquid phase extracting solvent. In Fig. 1, three extraction columns are shown but it is apparent that the number may be increased or decreased as conditions such as' efliciency of the extraction, the volumn of materials to be treated, etc., require.

Aiter extraction in tower I the rafiinate vapors pass from the top of the tower through line 8 to the bottom of extraction tower 9. The raflinate from extraction tower 9 likewise passes through line to tower II where the raflinate hydrocarbons, still in vapor phase, are again extracted by the selective solvent. The final vapor phase raflinate flows from the top of extraction tower ll through conduit l4 and control valve l5 to heat exchanger 2 where partial condensation occurs. Provision is made for returning a portion or all of the partial condensate from heat exchanger 2 through valve controlled line It to either extraction tower 9 or I I or both by means of independent return pipes controlled by valves l1 and I8 therein. The remaining rafilnate is cooled in condenser l9, condensed to liquid phase and passed to storage. Valve controlled conduit ISA provides means for supplying additional condensate tor reflux when the desired reflux ratio is higher than that obtainable by using the partialcondensate alone. I

The selective solvent which has been referred to in the previous paragraphs, flows through extraction columns I, 9 and II- counter currently to the -vapor phase petroleum being extracted. Fresh solvent is admitted to the top of tower ll through inlet line 29 controlled by valve A. The solvent flows down through the column and extracts those hydrocarbons for which it has a selective action i'rom the upwardly flowing vapor phase petroleum. The solvent with the selectively dissolved petroleum vapors "is continuously removed from the bottom of thecolumn through line 2| tovaporizer 22. To obtain more eflicient extraction it is desirable to heat the solvent in a vaporizer such as 22 in order to vaporize a substantial proportion of the dissolved hydrocarbons and re-circulate these vapors to the extraction column. This procedure tends to eliminate hydrocarbons oi the. railinate type which have condensed or which have been dissolved in the solvent. Also, the re-circulation of these vapors provides a method of adding heat totower I I.

ly extracts petroleum vapors in tower 9 and flows through line 25, heater 2B and line 21 to the top of tower I in the same manner as in the reviously described extraction step. Fromthe bottom of extraction tower 'I the solvent together with the dissolved hydrocarbons is removed through line 3| to vaporizer 32 where a small portion of the dissolved hydrocarbons is vaporized and returned to the extraction tower I through line 33. The selective solvent, and extract then ilow from the vaporizer 32 through valve 34 and line 35 to fractionating still 96. The extracted hydrocarbons are separated from the selective solvent by distillation and are removed from the top of the iractionating column through line 31, passed through heat exchanger 3 and condenser 38 to storage.

The solvent is continuously re-circulated from still 35 through line 20 to the extracting system as previously described. New or additional solvent can be supplied to the system as needed through valve controlled line 39 from the solvent. storage tanks. It is to be noted at this point that the solvent entering the extraction system from the still 36 is heated to a temperature above the boiling point of both the extract and raflinate. The temperature of the solvent in the extraction towers must of course be maintained below that at which a major proportion of the extract would be vaporized from'or remain undissolved in the solvent while being extracted. This temperature is, however, above the normal dew point of the extract as well as of the rafllnate hydrocarbons at the pressure existing in the system.

An auxiliary line 28 leading from vaporizer 5 and a control valve 40 are provided so that the petroleum vapors may be introduced into extraction tower 9 rather than into extraction tower I. When the vapors are so introduced, control valve 40 will be open and valve l2 in vapor line Ii will be closed. It is also apparent that the incoming hydrocarbon vapors may be The solvent, after being heated in vaporizer 22, flows through line-23 into the top of extraction tower I. The solvent then counter currentintroduced in both towers I and 9 by opening both valves 40 and I2.

Under various conditions it is desirable to remove side streams or cuts from the extracts of the different stages of extraction. Accordingly, valve controlled conduits 4| and 42 have been provided for this purpose and permit the removal 01' extract cuts fromv extractors 9 and II 'respectively. The portions 01', extract removed through these conduits will be separately distilled in a iractionating still similar to 36 shown in Figure 1 to separate the extracted compounds from the solvent; These additional stills have been omitted from the flow sheet for the sake of simplicity.

By controlling the conditions oi extraction in the various stages it is possible to obtain an extract from treater I which is substantially free from sulfur compounds and which is predominantly or entirely aromatic in chemical constitution. Likewise, by proper control an extract cut from treater 9 which contains a high proportion of sulfur bodies present in the petroleum-and an extract cut from treater II which is predominantly naphthenic in character may be obtained. In order to obtain these results it is of course necessary to maintain the temperature in treater I above the boiling point of the sulfur bodies, naphthenic compounds and paraflinic compounds in the petroleum, but within the range at which aromatic compounds are preferentially extracted by the selective solvent. In a similar manner the temperature inextractor 9 will be above the boiling point 01' the naphthenes and but within the range at which sulfur compounds are treated. with a given solvent anda given stock the proper conditions can be readily determined by experiment.

In view of the above discussion it is apparent that by the process represented in the flow sheet of Fig. 1 a petroleum fraction can be continuously separated into four separate fractions of distinctly different chemical constitution by passing the petroleum fraction through a series of three or more extraction zones, passing a liquid phase selective solvent through each of said extraction zones, intimately contacting the petroleum and the selective solvent in said extracting zones, maintaining said selective solvent in each of the zones at a temperature no lower than the boiling point of the petroleum fraction under the conditions of extraction in that zone, maintaining the temperature of the solvent above the boiling point of the non-aromatic compounds in the first zone of extraction but below the point at which all aromatic compounds would be vaporized from the solvent, maintaining the temperature of the solvent in the second extracting zone above the boiling point of the paraflinic and naphthenic compounds but below the point at which all s'ulfur bodies would be vaporized from the selective solvent and maintaining the temperature 01' the solvent in a third extraction zone above the boiling point of the paraflinic compounds, but within the range at which substantially all the cyclic non-benzenoid compounds are selectively dissolved. The paraifinic' compounds will then be removed in vapor phase from the third extraction zone and aromatics, sulfur bodies and naphthene compounds in the extracts from extraction zones 1, 2 and 3, respectively.

An added refinement which may be utilized in the process illustrated by Fig. 1 comprises operating extraction towers I, 9 and I l at successively decreased temperatures and pressures. In this species of operation extractor I will be maintained at substantially atmospheric pressures, for example, extractor 9 at an intermediate reduced pressure and extractor II at the lowest pressure and highest vacuum. Vacuum can be produced by theuse of condenser l9 and pump 45 or by other suitable and well-known arrangements 01' apparatus. Throttle valves 43 and H in vapor lines 8 and ill respectively are utilized to efiect a pressure differential between extractors 9 and H. Pumps 45 and 41 in lines 21 and 23 serveto feed the solvent from the zones of lower pressure to the zones of successively higher pressures. Pump 48 is provided in the reflux line to extractor 9 to feed the reflux from line Hi to extractor 9. This pump is necessary when as in the case of the from the bottom or tower 51 through line 58 'to vaporizer 5!. -A portion only or the extract is flashed into vapor form and re-circulated through line 50 to tower 51. Solvent is continuously removed from vaporizer 59 through line GI and passed to still 62 for removal of the extracted hydrocarbons. The extract is separated from the solvent in fractionating column 63 and flows through line 64, heat exchanger 53, line 65 and condenser 66 to storage. The selective solvent is continuously removed from the still and recirculated to extraction tower 51 through valve controlled line 61. The liquid level in the vaporizers 55, 59 and 62 is maintained above the conduit connections 54, 58, GI and 61 to produce a liquid seal and prevent the flow of vapors through these conduits.

Rafllnate vapors flow from the top or extrac-' tion tower 5'! through line 68 to heat exchanger 5| where partial condensation occurs. As much of this partial condensate as is desired may be returned. to the extraction tower through line 10 controlled by valve II. The remainder of the railinate passes through condenser 69 to storage. Valve controlled conduit 12 provides means for supplying additional condensate to the reflux line when the desired reflux ratio is higher than that obtainable with the partial condensate alone.

In a single stage extraction process it is essential that the vapor phase hydrocarbons and liquid present species of operation extractor 9 is operphase solvent'be intimately contacted. One efllcient means for effecting this result comprises the conventional bubble cap fractionating column inwhich the vapors to be extracted rise upwardly through a series of bubble caps and are thereby intimately mixed with the downflowing extracting solvent. Such an extraction tower is the preferred form utilized in the process of both Figs. 1 and 2.

To illustrate the characteristics of the process the following data are given:

A natural petroleum out having a boiling range of 200 to 300 F. was extracted in a single bubble cap tower with an arrangement of apparatus similar to that illustrated diagrammatically in Fig. 2. The data 01 a typical run using crude xylenols which had been topped at 450 F., as the selective solvent are given below:

Rate of petroleum feed 5 cc./min. Rate of solvent feed 25 cc./min. Temperature at base of extraction column 288 F. Temperature of rafiinate vapor 216 F. Temperature of still 490 F. Temperature of extract vapor from stripping column 249F. Temperature of solvent entering extractioncolumn 254 F. Temperature of stock entering column 245 F. Reflux ratio of rafiinate 1.9 Extract yield 38% Aniline point of stock fed 44.4 F. Aniline point of raflinate F. Aniline point of extract 15F.

In this run the temperatures or feed and selective solvent were to 10, and 10'to 20, respectively, above the dew point of the stock.

A series of tests was run to determine the effect of reflux of the rafllnate on the aniline point spread and yield 01 extract. Two series of data mum reflux ratio is zero. At that ratio the ani-.

sane

volved and that the less volatile raillnate hydrocarbons having a boiling point 20 to 60' higher than that of the extract hydrocarbons would be almost quantitatively separated as a vapor phase.

There is, 01' course, a practical limit to the range of boiling point spread between the extract and ramnate hydrocarbons which is permissible if pure'aromatics are to be obtained by selective solvent extraction in the vapor phase. When parafllnic and aromatic hydrocarbonsare being separated, those parafllnic hydrocarbons having a boiling point more than 100 F. above the boiling point of. the aromatics are dissolved in the solvent and will be removed with the extract in line point of the extract is as low-as can be oba v por phase extraction process. Parafline hytained with that particular extract-yield and soldrocarbons having boiling points to 60 F. vent stock ratio. The lower the yield, of course. ove e l g point oi thearomatics being the lower the aniline point or the extract. xtr ted a on th other a d. be fl v r When the optimum reflux ratio or zero is used, as mmnfite P it was found that the optimum ratio of solvent to 20 carbons having bplling ts e ual to or lower petroleum was approximately three to one. Ing g fi 'f g em present no creased ratios up to 'as high as five to one give ap- 3 f ever Ce 8 g traction procaa The ara evapor p ase. I n o erwo w on preciable benefits in the ex the paraflinic and naphthenic compounds present increased extractmn which results in the petroleum out have boiling point; no more from solvent ratios above five to one are rela than 600 R above the lowest boning aromatic tively small. which is extracted, an extract free from these In an arrangeme t of app Such s Shown higher boiling compounds can be produced. in g. 2 where the S ill 62 is separated from the Table No. 1 illustrates results obtained with extraction column by l qu d seals 50 at extra diiferent solvents in treatments on different types vapors cannot return to the extraction column, of petroleum oils.

Table 1 Extract Raillnate Solvent aniline aniline note natural petroleum stock trtsted p211, py ifggfit P211113, 21.? 0 m} .cut Calii'.crude.. 44.3 40 -44.4 110.2 so 1 44.3 18 -m4 81.8 as 1 44.3 -zo.4 114.4 so 1 42.5 19 +11.a 44 a 1 30.4 26 15.2 41.5 5 1 3 4 i 13.3 E 3.0 "i)'i?i'f 1f.f:::::::::3:13:33:::::: timeout crude iii 39 -301 m u a "Apparatus provided with liquid drocarbons having a boiling point as.much as F. above the boiling point of the aromatic hydrocarbons being extracted. In ordinary selective solvent liquid phase extraction processes. selectivity decreases with increase in temperature. At temperatures of 400 to 500 R, such as are involved in the process of this invention, selective solvents have heretofore beenregarded as entirely ineifective since they dissolve the raillnate hydrocarbons practically as readily as the extract hydrocarbons obtained at lower temperatures. Also, it is a generally accepted principle that as between two solutes dissolved in a given solvent, the higher the'boiling point of a given solute the less is its tendency to vaporize from the solution. That is, the lowest boiling dissolved hydrocarbon components should most readily vaporize from the solvent and the higher boiling hydrolectively dissolved at the high temperatures inbetween extraction and extract stripper columns.

from a California crude, the aniline point of the stock being 44.3 under conditions wherein phenol was employed as the selective solvent and the yield of extract held to 18%. Aniline point is a well-known measure of aromatic content, and the low aniline point of 75.4 F. is indicative of the purity of the product respecting relative absence of non-aromatic materia.

A selective solvent useful for the present process should be highly selective and should have a boiling point well above the end point of the stock to be treated. A boiling point above approximately 300 F. will generally be found desirable for extraction of normally liquid low boiling hydrocarbons. Preferably the solvent should not form constant boiling mixtures with hydrocarbons, but if such constant boiling point mixtures are formed, the solubility characteristics of the solvent should be such that complete recovery by water extraction is possible. Constant boiling mixtures of the solvent with water should not be formed or additional complications will rsult from the use of water in solvent recovery. Various solvents with the above desired properties have been .found and are listed in Table No. 2.

In order to test the relative selectivity of solvents a simple comparative, test wasadopted. This test consisted of adding a petroleum out slowly and with constant stirring so that the solvent could be maintained at'250 F. durin the test. A portion of the dissolved petroleum was vaporized from the mixture at this temperature and the first 3 cc. of overhead were taken for an aniline point test. The elevation of this aniline point over that Of the original stock is designated "selectivity".

"Table No. 2 lists the solvents tested in the order .10 tion at much higher temperatures than with the 200 to 300 cut, a 24 F. aniline extractwas produced and a total spread of aniline point between rafflnate and extract of 104.2 obtained.

In a, six hour test at 550 F., the maximum decomposition of the triethylene glycol was a change of 0.1% determined from 'bofling pointv curves of their selectivity as determined by this method.

Solvents having a selectivity factor greater than 25 are operative in the vapor phase extraction process of this invention providing they also have a boiling point substantially above the dew point of the hydrocarbon fraction being extracted. At-

tention is directed to the fact that this test merely indicates the relative selectivity of the solvents and that much greater aniline point spreads are obtained by the actual process of this invention. For example, xylenol has a selectivity of 32.1 as determined by the test but gave an aniline point spread of 103 F. between the extract and rat'- iinate when used to treat a 200 to 300 F. boiling point petroleum out (see Table 1).

Table 2 Selec- Solubiltivity lty' Solvent Remrninnl Diacetin "Chlorex 352 Dlaminopropanol Trieresyl phosphate Benzaldehyde 355 'grlethanolamine Diphenyl amine. v Acetophenone. 150 Xylenol 140 CarbltoY acetate 168 Butyl carbltoL. 130 Phenetldine 215 Dlbutyl phthalate. 410 at 20 mm 140 Number oi cc. of 2l5-240 F. straight run petroleum cut dissolved by 150 cc. of solvent at 250 F. and one atmosphere total absolute pressure.

Tetraethylene glycol and triethylene glycol have selectivity factors of 56.7 and 55 respectively. These solvents also have. very high boiling points and are highly eflicient selective solvents for vapor phase extraction.

Triethylene glycol is a preferred selective solvent for the present process.- It has a very high selectivity, is stable, non-corrosive and has the very high boiling point of 550 F. The high selectivity of this compound is illustrated by a run in which a petroleum stock having a boiling point range of from 200 to 300 F. was treated and an extract produced having an aniline point of -40 F. The spread of aniline point between the raflinate and the extract was l43.2- as compared with 103" with xylenol under the same conditions. Even with a 300 to 400 boiling range petroleum out, which necessitated extracssssssssssssessees taken before and after the test; Other tests failed to show any decomposition of the triethyleneglycol. The maximum corrosionobservcd on iron or steel was 0.008 inch per year at 550 F.

In a long run using the type of apparatus illustrated by Fig. 2 it was found that a small amount of trietrylene glycol distilled-over with the extract and raflinate fractions. The amount of triethylene glycol dissolved in the extract portion of the hydrocarbons was of the order of 0.15% by volume. This small amount of triethylene glycol is easily and completely removed by water washing and the solvent can then be recovered by the evaporation of the water. therefrom.

A more advantageous method for recovering the solvent from the wash water is to feed the water containing the solventinto vthe still and fractionating column along with the extract layer. Th s method has the advantage that it breaks up the constant boiling mixtures of solvents and high boiling extracts which may tend to form. The water and hydrocarbon extract come over as overhead and are readily separated. In those cases where there has been incomplete removal of water from the selective solvent, the effect is merely to render the solvent more selective in the extraction step of the process. That is, the antline point of the extract is lower and the yield of 4 aromatic hydrocarbons decreased.

As stated above, simple water washing completely removes even very minute amounts of triethylene glycol which may be dissolved in the petroleum. For example, it has been found that when a. 300 to 400 cut of. petroleum is contacted with a water solution containing 20% by weight of triethylene glycol, no detectable amount of triethylene glycol can be found in the petroleum layer. These data indicate that triethylene glycol has a very high partition coefficient between petroleum and water so that this solvent readily difiuses almost quantitatively from oil to water.

Tetramine constitutes an additional example of a selective solvent which is very eflicient in the process of this invention. This compound is one of a generic group which may'be represented by the general formula The first formula is an open chain compound exemplified by Diethylene triamine Triet'hylene tetramine (NH2' C2114 NH- C2H4'NH CzH-z-NHa) and tetraethylene pentamine (NHz'czHvNH-czHs-NH'CzI-I4-NH'CzH4'NH2) Examples of the second generic formula, which are ring compounds, are

Diethylene diamine e NHCzHuNH It will be noted that these compounds are characterized in that they conta n more carbon than nitrogen atoms in their molecules and can be formed by the inter-action of ethylene dichloride with ammonia followed by liberation of tree amine by treatment with caustic. These compounds wh ch have a boiling point above 300 F. are in general eminently suited for use as selective solvents in the process of this invention.

Although a number of specific examples oi suitable selective solvents have been given and although triethylene glycol is at present the preferred solvent for the process 01' this invention, it should be apparent to those skilled in the art that the broader aspects of the invention include the use of a multitude of other selective solvents. High boiling hydroxy ethers, illustrated by diethylene glycol, triethylene glycol and tetraethylene glycol, comprise one chemical type of selective solvent most suitable for the process herein disclosed. High boiling hydroxy esters, illustrated by diacetin, dibutyl tartrate, and butyl lactate, are also suitable. Carbitol acetate and butyl Carbitol illustrate operative compounds containing hydroxy, ether and ester groups.

Experiments indicate that polar compounds selected from the group consisting of hydroxy benzenes, amines, amides, chlorinated hydrocarbons, esters of polycarboxylic acids, and phosphoric acid esters of hydroxy benzenes are in general operative in the process of this invention. As previously pointed out the solvent selected from this group should have a boiling point sufliciently high so that it can be readily maintained in liquid phase under the conditions of extraction. In general, a boiling point above approximately 300 F. is desirable.

While the character of this invention has been described in detail and numerous illustrative examples given, this has been done by way of illustration only and with the intention that no limitation should be imposed upon the invention thereby. It will be apparent to those skilled in the art that numerous modifications and variations may be efiected in the practice 01' our invention which is of the scope of the claims appended hereto.

We claim:

1. A process of treating a petroleum fraction with a selective solvent which comprises passing a petroleum fraction containing aromatic, cyclic non-benzenoid and paraifinic compounds through a series of extraction zones, passing a high boiling liquid phase selective solvent through each of said extraction zones at a temperature substantially below its boiling point, intimately contacting the petroleum and the selective solvent in said zones, maintaining the selective solvent at a temperature no lower than the boiling point 01' the petroleum traction under the conditions of extraction, maintaining the temperature of said solvent above the boiling .point of the non-aromatic compounds in the first zone'of extraction and selectively dissolving aromatics in said solvent, maintaining the temperature of said solvent in a second extracting zone above the boiling point of the parafiinic compounds, and selectively dissolving cyclic non-benzenoid compounds in the solvent. and removing parafllnic compounds in 12 vapor phase from the last of said extraction zones.

2. A process of treating a petroleum'to selectively extract carbocyclic non-parafllnic hydrocarbons therelrom which'comprises passing said petroleumthrough succ'essive extraction zones,

passing a liquid phase selective solvent countercurrently to said petroleum through each 01' said extraction zones, maintaining the selective solvent in liquid phase and at a temperature above the initial boiling point of the petroleum fraction under the conditions of extraction, intimately contacting the petroleum and selective solvent in said zones and maintaining the vapor pressure in at least one of said extraction zones below that or the extraction zone in which the petroleum is first contacted with the selective solvent.

3. A process of treating petroleum to selectively extract non-parafllnlc hydrocarbons therefrom which comprises passing said petroleum through a series of extraction zones, passing a liquid phase selective solvent countercurrently through said zone, intimately contacting the petroleum and selective solvent in each of said extraction zones, successively decreasing the vapor pressure in said series of zones from a region of highest pressure at the petroleum inlet zone to a region of lowest pressure at the petroleum outlet zone, and maintaining the temperature of said liquid phase selective solvent in each of said zones above the boiling point of the petroleum at the pressure of extraction in that zone but substantially below the boiling point of the selective solvent.

4. A process which comprises extracting a petroleum fraction with triethylene glycol, separating an extract phaseand a raflinate phase, vaporizing dissolved hydrocarbons from said extract phase,- and adding water to said extract vaporizer to inhibit formation of constant boiling mixtures of said triethylene glycol and dissolved hydrocarbons ln said extract.

5. In a process of treating a hydrocarbon mixture with a selective solvent to selectively extract carbocyclic non-parafllnic hydrocarbons therefrom, the steps which comprise passing into an extraction zone a normally liquid hydrocarbon fraction containing a mixture of carbocyclic and parailinic hydrocarbons in which the least volatile paraflinic hydrocarbon normally boils from approximately 20 to 60 F. above the normal boiling point of the most volatile carbocyclic nonparaiilnic hydrocarbon in said mixture, passing a liquid phase selective solvent through said extraction zone, intimately contacting said hydrocarbon fraction in vapor phase 'with said liquid phase selective solvent, separating a vapor phase hydrocarbon rafllnate from said liquid phase selective solvent, maintaining said selective solvent at said point of separation above the intial boiling point'but no more than approximately 20 F. above the dew point or said hydrocarbon fraction under the conditions of extraction, passing the liquid phase selective solvent containing carbocyclic non-paraflinic. hydrocarbons from said extraction zone to an independent distillation zone, condensing said vapor phase hydrocarbon ramnate, and returning to said extraction zone approximately two-thirds of said condensed railina e. I

6. In a process of treating a hydrocarbon petroleum mixture with a selective solvent to selectively extract carbocyclic non-parafllnic aromatic hydrocarbons therefrom, the steps which comprise "passing into an extraction zone 13 liquid hydrocarbon petroleum fraction containing a mixture of carbocyclic and parafllnic hydrocarbons including aromatic hydrocarbons in which the least volatile parafilnic hydrocarbon normally boils from approximately 20 to 60 F. above the normal boiling point of the most volatile carbocyclic non-parafllnic aromatic hydrocarbon in said mixture whereby an extract free from these higher boiling-compounds can be produced, passing a liquid phase selective solvent downwardly through said extraction zone, intimately contacting said hydrocarbon petroleum- !raction in vapor phase with said liquid phase selective solvent, separating a vapor phase hydrocarbon rafllnate from said liquid phase selective solvent as a top product from said zone, maintaining said selective solvent at said point of separation above the initial boiling point but no more than approximately 20 F. above the dew point of said hydrocarbon fraction under the conditions of extraction, passing the liquid phase selective solvent containing carbocyclic non-parafllnic aromatic hydrocarbons from said extraccases tion zone to an independent distillation zone, condensing said vapor phase hydrocarbon rafllnate, and returning to the upper portion of said extraction zone approximately two-thirds of said condensed rafilnate. I

7. A process as set forth inclaim 6, wherein the least volatile parafi'inic hydrocarbon normally boils approximately 20 F. above the normal boiling point of the most volatile carbocyclic non-paraflinic aromatic hydrocarbon in said petroleum fraction.

8. A process as set forth in claim 7, wherein theleast volatile parafllnic hydrocarbon normally boils approximately 60 F. above the nor:

mal boiling point of the most volatile carbocyclic -non-para17inic aromatic hydrocarbon in said petroleum fraction.

CALIFORNIA By L. P. ELLIOTT,

Vice-President.

RESEARCH CORPORATION.

No references cited. 

